Postoperative pain relief obtained by the thoracic epidural injection of 5 or 10 mg morphine was assessed in two groups of elderly patients scheduled for abdominal surgery. In the first group of patients (n = 37, mean age 73.2 +/- 9.9 years), five epidural morphine provided a good and prolonged analgesia for an average duration of 24.5 hours. All patients showed a remarkable lucidity and remained fully cooperative when receiving chest physiotherapy. In the second group (n = 11, mean age 65.3 +/- 11.2 years), ten mg epidural morphine induced a more powerful analgesia lasting on average 38 hours. In this group however, fine patients developed a respiratory depression, often delayed in onset, associated with increased PaCO2 levels and/or bradypnea, requiring treatment with narcotic antagonists. Also an important degree of sedation was observed. These results emphasize the inherent dangers of ventilatory depression of high dose thoracic epidural morphine treatments in elderly patients.